The present invention relates generally to gas turbine engines, and, more specifically, to blisks therein.
A gas turbine engine includes various stages of bladed disks in the compressor and turbine thereof which pressurize air in the former and expand hot combustion gases in the latter. The compressor blades or turbine blades are typically mounted to their supporting disks by dovetails which are radially retained in corresponding dovetail slots in the rims of the disks.
Advantages in performance, manufacture, and weight may be obtained by integrally forming the blades and disks in a unitary or one-piece construction known as a blisk. In one method of manufacture, the individual blades and features of the supporting disk are machined from a common blank of metal. Complex three dimensional machining is required to precisely obtain the required aerodynamic flow passages between the blades.
Since blisks may be damaged in the normal course of operation in a gas turbine engine before their useful lives have been met, it is desirable to repair the blisks. However, since the blades are integrally formed with the disk, they are not readily individually removable in the manner of bladed disks having dovetails.
Accordingly, either portions of an individual damaged blade may be removed by machining and replaced with a corresponding blade piece, or the entire damaged blade may be removed and replaced. In either example, the repaired blisk should be returned as close as possible to its original strength for completing its original useful life without undesirable early termination thereof
Another form of blisk manufacture and repair uses translational friction welding for integrally welding individual blades to a disk. The disk is typically initially fabricated with a row of integral stubs extending radially outwardly from the rim of the disk. Each stub has a smooth weld surface which complements a corresponding smooth blade root for permitting friction welding therebetween.
Each blade initially includes a fixturing collar near the blade root so that compression and translation forces may be applied to the individual blade for developing friction at the weld surface as the blade is quickly oscillated during the welding process. The blade and stub material at the weld surface locally fuses to form a friction weld bond thereat, after which the resulting weld flashing and fixturing collar are removed by conventional machining for achieving the desired aerodynamic contour of the blade and rim surfaces.
Since the friction welding forces are substantial, the original rim stubs are provided oversize with excess material to prevent undesirable plastic deformation of the stubs and blade during friction welding. The excess material may then be removed by machining following the friction welding process.
However, in the event that repair of the blisk is desired and a complete blade must be removed, the remaining stub no longer includes the original excess material. The correspondingly smaller stub is therefore subject to undesirable deformation during the friction welding process of a replacement blade, which can damage the blisk and render it unusable for return to service in the engine.
Another problem with friction welding of blisks is the exposure to the environment along the edges of the weld surface as the blade is oscillated during welding. The original oversized stub and correspondingly oversized blade root provide additional surface area for decreasing the likelihood of environmental contamination at the resulting weld line. The excess material machined away after friction welding typically removes therewith any undesirable contamination around the weld surface. Since the stubs no longer have excess material for the repair operation, the weld surfaces are subject to environmental contamination.
These problems of typical friction welding are further compounded by the axial contour of the disk rim defining the inner flowpath boundary of the flow passages between adjacent blades. In a typical entry-stage configuration of a fan or compressor blisk, the blisk rim increases in diameter between its forward and aft ends, and typically has an arcuate contour therebetween which may have a generally S-shape. Accordingly, the stub weld surface typically follows the axial profile of the disk rim for maintaining the weld surface as large as possible.
Typical compressor blades have maximum thickness in their midchord regions, with correspondingly thin leading and trailing edges, and typically decrease in thickness from root to tip thereof. The rim stub and the blade root therefore typically have complementary arcuate weld surfaces for maximizing the surface area and reducing distortion during the friction welding process.
Since the weld plane is arcuate, both the rim stub and blade root require precise three dimensional machining to create closely matching surfaces for achieving complete friction welding. And, the arcuate weld surface can only be translated in the axisymmetric direction circumferentially around the disk rim. This circumferential or lateral frictional oscillation of the blade on its corresponding stub is rendered more difficult when conducted between two adjacent blades already welded to their stubs.
Accordingly, it is desired to provide a blisk having an improved configuration of the weld plane for advantages in both original manufacturing thereof as well as during subsequent repair.
A blisk includes a disk having a rim. A row of blades extends outwardly from the rim in a unitary construction. The blades are spaced apart in the disk rim to define fluted inner flowpath channels extending axially between the blades to bound corresponding flow passages therebetween.